Besides the flag that three firemen raised at Ground Zero, other important historical artifacts have been lost, and sometimes recovered:

• The 15th star on the "Star Spangled Banner" was cut out as a souvenir from the flag at Fort McHenry, Md., that inspired Francis Scott Key's anthem in 1814. The Smithsonian's National Museum of American History owns the flag.

• Jacqueline Kennedy's pink pillbox hat was part of her ensemble the day President Kennedy was assassinated in Dallas in 1963. Although the National Archives has the first lady's blood-spattered pink suit, the hat has disappeared.

• Astronaut Gus Grissom's space capsule, Liberty Bell 7, sat 3 miles below the surface of the Atlantic Ocean until it was found and pulled up in 1991. When Grissom splashed down 300 miles from Cape Canaveral after his 16-minute suborbital flight on July 21, 1961, the escape hatch blew open, flooding the capsule. Grissom was rescued by helicopter. The capsule sank. It now resides at the Cosmosphere space museum outside Wichita.

• A sixth copy of the Gettysburg Address was found folded inside a book at an Ohio anti-ques fair in 1990. Five copies in Lincoln's handwriting already were known to exist, including two in the Library of Congress. The sixth contained the final third of the short speech. It is signed "A. Lincoln."

• The "Rosa Parks Bus" languished for years in an Alabama field. Its owners had been told it was the bus on which Parks, a black seamstress, had refused to give up her seat to a white man in segregated Montgomery in 1955, but they had no documentation. An auctioneer established its authenticity for the Henry Ford Museum in Dearborn, Mich., which bought it for $427,919 in 2001.

NEW YORK  On April 1, 2002, a flag that had become the emblem of American resilience was unfurled in a solemn, wordless ceremony outside City Hall.

Hours after the 9/11 attacks, three firefighters had spontaneously used a U.S. flag taken off a yacht and raised it in the wreckage of the World Trade Center. A newspaper photographer captured the scene, creating a classic image.

Seven months later, the three firemen were guests of honor as the flag was run up the City Hall pole. But Dan McWilliams, one of the firemen, said softly, "That's not the flag."

Bill Kelly, the firefighters' lawyer, stared at him. "That's much bigger than the one we put up," McWilliams explained. Kelly says he looked at the other two firemen: "They said, 'No, that's not it.' " The men said nothing more, and the flag flew at City Hall for a week before beginning a tour of police stations and firehouses.

It was an impostor. Five years after 9/11, the day's most famous artifact is still missing.

"It's a piece of history," says Shirley Dreifus, owner of the yacht from which one of the firemen took the flag. "I don't think the average citizen knows it's missing."

The flag in the photograph taken on 9/11 by Thomas Franklin of The Record of Bergen County, N.J., was 3 feet by 5 feet. The one raised at City Hall — and flown at Yankee Stadium and on warships and once destined for the Smithsonian — is 5 by 8.

How did the flags get switched? Did someone replace the smaller with the larger at Ground Zero? If so, why? And what happened to the original?

Photo captured a moment

The three firemen raised the flag at the darkest hour of one of the darkest days in U.S. history. The twin towers were in smithereens. After six hours of searching, it was apparent there were few survivors.

As McWilliams walked past a yacht docked on the Hudson River, he spotted an American flag attached to a broken wooden pole. He grabbed it and walked back toward Ground Zero, joined en route by George Johnson, a member of his Brooklyn ladder company, and Billy Eisengrein, whom he'd known since they were kids on Staten Island.

At Ground Zero, the firefighters found a long metal flagpole jutting at a 45-degree angle from a ledge about 20 feet above the ground. They climbed up and began rigging the flag to the pole.

They never saw Franklin, who took the picture from about 100 feet away. As he was shooting, he thought of the famous photo of the flag-raising on Iwo Jima in 1945.

The Record sent the photo to the Associated Press — and through its network to the world. Over the next year the image appeared on U.S. commandos' "calling cards" on the battlefields of Afghanistan, on a postage stamp, on the side of a barn in Upstate New York.

Within 10 days after it was raised, the flag — or rather, a flag — was taken down by the fire department; the Navy wanted to borrow it for display on the carrier Theodore Roosevelt, heading to the Arabian Sea off Afghanistan.

On Sept. 23, the same flag appeared at a service at Yankee Stadium, where it was signed by Gov. George Pataki, Mayor Rudy Giuliani and the fire and police commissioners. Then it was flown off to the Roosevelt.

In January 2002, Shirley Dreifus called USA TODAY to say the flag came from the yacht Star of America, owned by her and her husband. The firefighters signed an affidavit confirming that claim.

In March, as the carrier returned to Norfolk, Va., Johnson and Eisengrein were flown onboard to accept the flag, folded in a triangle, on behalf of the city.

That summer, Dreifus asked the city to borrow the flag for a firefighters' fundraiser on the yacht. When she got the flag, she realized it was too big to have been the yacht's.

"I don't doubt it flew at Ground Zero," Dreifus says of the larger flag — it even smelled of smoke. "It just wasn't the one from our boat."

Pressing the search

They demanded that the city find the right one. In what Dreifus describes as an attempt to "put some energy" behind the search, they sued the city for $525,000 — the price at which appraisers valued the flag, which originally cost $50.

The city couldn't find the flag, and the suit was dropped. Mayor Michael Bloomberg said he didn't know where the flag was: "I don't know where Osama bin Laden is, either."

Coincidentally, two flags also were raised on Iwo Jima by different groups of servicemen. The second, larger one was in the Associated Press photo; both are in the Marine Corps collection in Quantico, Va.

David Friend, a Vanity Fair editor and author of a new book on the visual images of 9/11, says he believes the flag was switched within days.

The three firemen have declined interview requests over the past five years. But Friend's book, Watching the World Change, quotes Billy Eisengrein as saying that while working at Ground Zero a few days after 9/11, he noticed the flag was gone from the pole: "Who took it down, I have no idea."

Was the first flag replaced because it was too small? Was it lowered when it began to rain and innocently switched with another flag found at the site? Did someone in the fire department not want to let the Navy borrow it? Once the photo appeared on the front page of the New York Post on Sept. 13, did a thief realize its value? Was Ground Zero in the week after the attack still sufficiently chaotic to allow someone to take the flag unnoticed?

Dreifus keeps an eye on the Internet to make sure no one tries to sell it: "I think whoever took it down must know what it was."

Brooklyn firefighters George Johnson, left, of Ladder 157, Dan McWilliams, center, of Ladder 157, and Billy Eisengrein, right, of Rescue 2, raise a flag at the World Trade Center in New York in this Sept. 11, 2001 file photo. The flag, the day's most famous artifact, has been missing for five years.